Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Em qual site a Northwestern foi adversária?
 ###Tabelas: CREATE TABLE italy (italy_id AUTO_INCREMENT PRIMARY KEY, Actor VARCHAR, Character VARCHAR, Soap Opera VARCHAR, Years VARCHAR, Duration VARCHAR) CREATE TABLE comparison_chart (comparison_chart_id AUTO_INCREMENT PRIMARY KEY, Project VARCHAR, License VARCHAR, Date VARCHAR, Protocol VARCHAR, Technology VARCHAR, Server VARCHAR, Client VARCHAR, Web Client VARCHAR, Multiple Sessions VARCHAR, Encryption VARCHAR, Authentication VARCHAR, Data Compression VARCHAR, Image Quality VARCHAR, Color Quality VARCHAR, File Transfer VARCHAR, Clipboard Transfer VARCHAR, Chat VARCHAR, Relay VARCHAR, HTTP Tunnel VARCHAR, Proxy VARCHAR) CREATE TABLE former_members (former_members_id AUTO_INCREMENT PRIMARY KEY, School VARCHAR, Location VARCHAR, Mascot VARCHAR, County VARCHAR, Year Joined VARCHAR, Previous Conference VARCHAR, Year Left VARCHAR) CREATE TABLE schedule (schedule_id AUTO_INCREMENT PRIMARY KEY, Date VARCHAR, Opponent# VARCHAR, Site VARCHAR, Result VARCHAR, Attendance VARCHAR) CREATE TABLE owned_and_operated_stations_of_other_networks (owned_and_operated_stations_of_other_networks_id AUTO_INCREMENT PRIMARY KEY, City VARCHAR, State or Territory VARCHAR, Station call sign VARCHAR, Network VARCHAR, Channel number INT, Programs Aired VARCHAR)  
SELECT Site FROM schedule WHERE Opponent# = northwestern